This invention is concerned with acceleration engineering, especially induction acceleration, and might be used as a commercial-type compact accelerator of charged particles for the formation of singular and multiple relativistic beams of charged particles, including beams of different energy and charge characteristics.
There is known an induction accelerator, which can be used as a device for the formation of singular electronic relativistic beams [Redinato L. “The advanced test accelerator (ATA), a 50-MeV, 10-kA Inductional Linac.” IEEE Trans., NS-30, No 4, pp. 2970–2973, 1983]. This device is called also the one-channel linear induction accelerator (OILINAC). The OILINAC is composed of an injector block, acceleration block, drive source, and output system. Its peculiarity is that the one-channel linear induction acceleration block is made in the form of a sequence of linearly united acceleration sections, which form, in turn, a linear accelerative working channel. The acceleration of the charged particle beam is achieved by the effect of accelerative action of longitudinal vortex high-frequency (tens MHz) electric field, which is generated within the working channel by alternating with time current in special inductor windings. The averaged energy rates of the acceleration for OILINAC are ˜0.7–1.5 MeV/m. For example, in the above-mentioned design of OILINAC [Redinato L. “The advanced test accelerator (ATA), a 50-MeV, 10-kA Induction Linac.” IEEE Trans., NS-30, No 4, pp 2970–2973, 1983] the averaged acceleration energy rate is ˜0.7 MeV/m. The other characteristic of the OILINAC is that only one electron beam is accelerated on all stages of the acceleration process.
Large linear dimensions, limited functional potentialities, and a limited current strength of the accelerating beam are the basic shortcomings of the OILINAC.
The large dimensions (e.g. 60–70 m length for OILINACs of the ATA class) cause severe complication of total infrastructure of its accommodation and service (it needs special accommodation, radiation-protection systems and service, etc.). As a result, the commercial application of the OILINAC as a basic design element for various types of commercial devices becomes economically unsuitable because of cost involved.
Practicality is predicated upon the formation of charged-particle beams with multi-component structure. For example the two-velocity electron beams for the superheterodyne free-electron lasers, complex (electron-ion or ion-ion) beams for some technology systems, etc. A direct use of OILINAC in such situations is impossible, since, as it was mentioned before, they are designed for the formation of exclusively one-energy and one-component relativistic beams of charged particles.
The limitation of the current strength of the beam is related with the increasing role of the beam instability at an increase of its density. Consequently the formation and the acceleration of long beams of tens kA's becomes technologically a very complicated problem and the formation of a many hundreds-kA beams becomes practically impossible.
There is also known an induction accelerator, which can work as a device for the formation of relativistic beams of charged particles and which is named the multi-channel induction linear accelerator (MILINAC) [V. V. Kulish, A. C. Melnyk. Multi-channel linear induction accelerator, U.S. Pat. No. 6,653,640 B2; issued Nov. 25, 2003.]. The MILINAC consists of an injector block, acceleration block, drive source, and output systems. Here the acceleration block consists of at least two one-channel linear induction acceleration blocks of the OILINAC (one-channel block); the injector block comprises one or more injectors, each of which is linked to an individual one-channel block. The charged-particles output systems are attached to the output systems of one-channel blocks. A design feature peculiarity of the output systems allows simultaneous acceleration of several separate charged particle beams. The output systems can have a form of systems for merging together the accelerated beams. It can bring together the beams of the same kind of charged particles as well as of different kinds of particle beams.
The above design overcomes a part of the noted above shortcomings of the OILINAC. This happens basically therefore that the MILINAC can drastically increase the total current of the accelerated multiple beams. Besides this MILINAC has a wide field of functional possibilities. This includes the formation of the two- and multi-velocity electron beams, combination electron-ion and ion-ion beams, beams of different kind of ions, e.g. positive and negative ion beams, etc.
Like in the case of OILINAC, the basic shortcoming of the MILINAC is its essential longitudinal dimensions, which are more pronounced when energies of accelerated beams become higher than ˜10 MeV.
There is also known an induction accelerator, which is able to work as a device for the formation of the relativistic beams of charged particles [V. V. Kulish, P. B. Kosel, A. C. Melnyk, N. Kolcio Induction Undulative EH-Accelerator, U.S. Pat. No. 6,433,494 B1, issued Aug. 13, 2001]. It is also referred to as the multi-channel induction undulative accelerator (MIUNAC) or the EH-accelerator. This multi-channel undulation induction accelerator of charged particles comprises an injector block, drive source, output systems, turning systems, and an induction acceleration block. The latter block is made in the form of at least two one-channel linear induction acceleration blocks (including those that are placed parallel with one to other). The one-channel linear induction acceleration blocks are linked by means of the turning systems, each of which connects the output of one of the one-channel linear induction acceleration blocks with an input of another similar block. This does not concern those inputs, which are connected with injectors; and those outputs, which are destined for coming out the accelerated partial beams.
The method describing connection of the one-channel linear induction acceleration blocks and the turning systems gives an undulative-like form of the working acceleration channels in the MIUNIAC. This means that the charged-particle beams pass the undulative acceleration channels by undulative trajectories. That is why this class of accelerators is named as undulative accelerators.
The output systems are attached to the outputs of the undulative acceleration channels. A characteristic of this design is that the turning systems are made from bipolar permanent magnets or permanent (or quasi-permanent) electromagnets.
The advantage of the discussed design solution results in the compactness of the EH-accelerators and its lower cost as compared with the two other types accelerators. For example, in a case that EH-accelerator is built on the basis of the one-channel acceleration blocks ATA-type (OILINAC), then when constructed with 5 turnings the total length of the system decreases e.g. from, for instance, 60 m to 10 m.
Like the MILINAC, the EH-accelerators are suitable for a simultaneous acceleration of a few charged-particle beams, including the beams composed of different kind of charged particles.
The shortcomings of the known design solution are: large current losses of the beam during the acceleration process, low efficiency, and limitated current of the accelerated beam.
The large losses of the beam current are caused basically by the imperfect structure of the turning systems. As it was mentioned above, they are based on two-polar magnets. This shortcoming of the EH-accelerators is manifested primarily as significant losses in beam current in the process of its transportation through the undulative acceleration channel. These losses are caused by the effect of three physical mechanisms.
The first of these mechanisms is related with the beam-dispersion effect in the magnetic field of the turning system. The essence of the effect is in the following: The real charged particle (for instant, electron) beams, which are formed by the injectors, exhibit always some distribution of energy of the particles. As a consequence, the turning radii of different electrons in the working space of the turning magnets exhibit electron scattering that depends on the turning radii. This means that the specific dimension of a beam at an entrance to each turning is smaller than its dimension at the outlet. As a result of this, with each turning the amount of the particles, which in the process of acceleration “doesn't join” into the geometry of the subsequent linear acceleration channel, increases. These particles systematically settle down on the walls of this channel entrance.
The second of the above-mentioned mechanisms is related with the Coulomb's repulsion of the beam charged particles. An additional displacement of the particle trajectories within the cross-section of a turning is caused by the Coulomb's repulsion. This increases additionally the amount of particles, which doesn't get into cross-section channel and remains beyond the acceleration channel. Because of this, to achieve a turning for a beam having a beam current strength higher than ˜100 A is practically not realistic. Hence, the second mechanism of the loss of the beam current is related with the limitation of the beam-current strength in the acceleration channel.
The third physical mechanism of the loss is related with an increased inclination for the instability excitation in a beam at an increase of beam current strength. The beam looses its shape and finally is settling down on the walls of a channel as consequence of this instability. One should stress that the probability of the development of instability is larger the lower is the energy of beam's charged particles. Therefore, in the process of acceleration the probability of beam-instability development decreases. Consequently, like in the case of the previous mechanism, this mechanism limits the current intensity that can be accelerated in the EH-Accelerator. As it follows from the said above, these limitations are more pronounced in the first one-channel acceleration blocks.
Specific features of the turning systems of the EH-accelerator results in their low efficiency. The turning systems, which are used, are suitable to turn a beam for 180° without losses only in the case of the electron-beam current up to ˜50 A. However, at an additional increase of current strength (˜100 A or higher) the beam is unable to pass through the two-polar magnetic turning systems without scattering. This phenomenon was already discussed above. It is well known that the basic total losses of energy in the OILINAC and MILINAC-type induction systems are due to the demagnetization of the inductor cores. Moreover, these losses are weakly dependent on the current strength of the beam, which is undergoing acceleration, and they basically depend on the core material. This means automatically that the suitable values of the efficiency cannot be achieved at all for the known design of EH-accelerator because of the mentioned limitation of the beam current.
Following is a more detail explanation of the conclusion obtained: the energy losses in the core practically are independent, as it is mentioned, of the current strength of the accelerating beam. The energy, which is transferred to the beam in the process of acceleration, should be treated as the useful energy. As it is well known, this energy is directly proportional to the current strength of the beam. These relationships determine the main way of an increase of the EH-Accelerator efficiency. The experience showed that at ˜1 kA beam current strength, the losses within the core are approximately equal to the energy obtained by the beam in the process of the acceleration. Therefore, the high efficiency of the OILINAC-type electron accelerators can be realized only in a case of high current strength, >1 kA. As it was shown before, at this strength electron beams cannot pass through the turning systems in this case of EH-accelerators because of the above-discussed limitations for beam current.